程式原始碼
var floatAd = {}; floatAd.getScrollTop = function(node) { var doc = node ? node.ownerDocument : document; return doc.documentElement.scrollTop || doc.body.scrollTop; }; floatAd.getScrollLeft = function(node) { var doc = node ? node.ownerDocument : document; return doc.documentElement.scrollLeft || doc.body.scrollLeft; }; floatAd.getBrowser = function() { var d = document.documentElement; return { width: window.innerWidth || (d && d.clientWidth) || document.body.clientWidth, height: window.innerHeight || (d && d.clientHeight) || document.body.clientHeight } }; floatAd.extend = function(destination, source) { for(var property in source) { destination[property] = source[property]; } return destination; }; /* 默认属性扩展 */ floatAd.setOptions = function(options) { this.options = { delay: 20, // 调整速率 fadeTime: 1 // 自动消失时间 }; return this.extend(this.options, options || {}); }; /* 类初始化 */ floatAd.init = function(id, options) { var _this = this; this.extend(this, this.setOptions(options)); this.control = document.getElementById(id); var _callback = function() { // fadeIn完成后的回调函数 _this.timer = window.setInterval(function() { _this.scroll() }, _this.delay); // 滚动定位 window.setTimeout(function() { _this.fadeOut() }, _this.fadeTime * 1000); // 在固定时间内消失 } this.fadeIn(_callback); window.onresize = function() { _this.setCenter(); } }; /* 定时滚动 */ floatAd.scroll = function() { this.start = parseInt(this.control.style.top, 10); this.end = parseInt(this.getScrollTop() + this.getBrowser().height - this.control.clientHeight, 10); if(this.start != this.end) { this.amount = Math.ceil(Math.abs(this.end - this.start) / 15); /* 递减公式(this.start无限增大,整个分子无限减小,整个值就无限趋近于0) */ this.control.style.top = parseInt(this.control.style.top, 10) + ((this.end < this.start) ? -this.amount : this.amount) + 'px'; } }; /* 目标居中并处于最底部 */ floatAd.setCenter = function() { this.top = this.getScrollTop() + floatAd.getBrowser().height; this.left = (this.getScrollLeft() + floatAd.getBrowser().width - this.control.clientWidth) / 2; this.control.style.top = this.top + 'px'; this.control.style.left = this.left + 'px'; }; /* fadeIn */ floatAd.fadeIn = function(callback) { var _this = this, _top = 0; this.control.style.display = 'block'; // *要提前显示.不然无法取得clientWidth this.setCenter(); var _timer = window.setInterval(function() { _this.control.style.top = _this.getScrollTop() + _this.getBrowser().height - (++_top) + 'px'; if(_top >= _this.control.clientHeight) { window.clearInterval(_timer); callback && callback(); } }, 2); }; /* fadeOut */ floatAd.fadeOut = function() { var _this = this, _num = 0, _top = _this.control.clientHeight; window.clearTimeout(this.timer); var _timer = window.setInterval(function() { if(_top <= 0) { window.clearInterval(_timer); _this.control.style.display = 'none'; } else { _this.control.style.top = _this.getScrollTop() + _this.getBrowser().height - (--_top) + 'px'; } }, 2); this.control.style.top = (parseInt(this.control.style.top, 10) + 100) + 'px'; }; var newAd = 'start'; document.getElementById('show').onclick = function() { if(newAd == 'start') { newAd = floatAd.init('ad', { fadeTime: 10 }); } }
程式原理
整個廣告運行具有四步驟動作.
1. 初始化時隱藏於頁最底部.
2. 自底向上升起.直到整個廣告漂浮出來
3. 啟動偵測
2. 自底向上升起.直到整個廣告漂浮出來
3. 啟動偵測.保持廣告始終處於頁面中間最底部.
4. 到達自訂間隔時間.廣告自動漸隱.
整個實現最重要的就是控制廣告距離文檔(非視窗)最頂部的距離.(scrollTop + browser.clientHeight) .這裡提供了獲取這幾個值的代碼.
注意Chrome和Safari即使在標準doc模式下的根文檔也是document.body而不是document.documentElement
floatAd.getScrollTop = function(node) { var doc = node ? node.ownerDocument : document; return doc.documentElement.scrollTop || doc.body.scrollTop; }; floatAd.getScrollLeft = function(node) { var doc = node ? node.ownerDocument : document; return doc.documentElement.scrollLeft || doc.body.scrollLeft; };
floatAd.getBrowser = function() { var d = document.documentElement; return { width: window.innerWidth || (d && d.clientWidth) || document.body.clientWidth, height: window.innerHeight || (d && d.clientHeight) || document.body.clientHeight } };
預設屬性有:
delay: 20, // 调整速率 fadeTime: 1 // 自动消失时间(s) var newAd = 'start'; document.getElementById('show').onclick = function() { if(newAd == 'start') { newAd = floatAd.init('ad', { fadeTime: 10 }); } }
這裡為了示範方便.所以當點擊按鈕時候才初始化廣告.也可以在window.onload的時候就載入廣告.
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